1. Field of the Invention
The present invention relates to a defect compensation method for compensating for a defect generated at a surface of a plate formed of a transparent material such as glass without spoiling the light transmitting property thereof. In particular, the present invention relates to a defect compensation method for compensating for a microscopic concave defect at a display plane of a display apparatus such as a liquid crystal display apparatus.
2. Description of the Related Art
When a linear or point concave defect such as a flaw, a scratch, a crack or the like is generated at a display plane of a display apparatus or the like, light radiated to the display plane is scattered or reflected by the defect, thereby adversely effecting the resultant display. In order to avoid such an inconvenience, defect compensation is performed for avoiding such a concave defect from effecting the display.
Conventionally, the defect compensation is performed in the following manner. By rotating a buff or the like coated with fine rubbing powders or by rotating a grinder coated with a rubbing liquid including rubbing powders, a portion including the concave defect is mechanically rubbed and thus removed by friction. Since such methods involve the following problems, a surface obtained by this type of defect compensation is not satisfactory. Hereinafter, the surface obtained by the defect compensation will be referred to as a "processed surface".
(1) Powders chipped away from the display plane formed of glass or the like and the rubbing powders splashed by rubbing causes problems in terms of cleanliness of the operational environment. PA1 (2) In the case where the display plane is combined with a substrate including an LSI or the like, the LSI may be destroyed by vibration caused by rubbing. Further, static electricity generated by rubbing friction may destroy a thin film transistor or a driving circuit provided in the substrate. PA1 (3) Powders of glass which have been rubbed off or rubbing powders enter the display apparatus to cause a display malfunction. PA1 (4) The rubbing process requires a long period of time, which increases the compensation cost. PA1 (5) Since the display plane treated with rubbing becomes rough with microscopic ruggedness, the light transmitting property of the display plane is spoiled. This fact provides another display defect.
Recently, the use of excimer laser for smoothing a portion including the defect has been developed. For example, examples of utilization of excimer laser for precise processing of a polymer film or a ceramic material or for marking at a plastic or ceramic material are described in "Excimer Laser niyoru Bisai Kako eno Ohyo (Utilization of Excimer Laser for Precise Processing)" in Ohyo Kikai Kogaku (September, 1990). The processing described in this article is used for forming a hole, cutting, marking or the like, but not for smoothing the processed surface in order to reliably maintain the light transmitting property, which is indispensable for the defect compensation of a transparent plate of a display apparatus.
The use of a laser beam for the defect compensation in a liquid crystal display apparatus has also been developed. For example, Japanese Laid-Open Patent Publication No. 3-126913 discloses a method for separating a pair of substrates of a liquid crystal display apparatus by radiation of a laser beam. This method, according to which the laser beam is transmitted through the substrates, cannot be used for the defect compensation of the substrate itself. Japanese Laid-Open Patent Publication No. 3-265820 discloses a method for compensating for a defect by radiating a laser beam to a surface of a substrate of the liquid crystal display apparatus. According to this method, the surface is roughened to make a portion including the defect non-transparent, but not smoothed. The rough surface obtained by this method does not have a satisfactory light transmitting property, which may provide another defect.